Abstract
The BeiDou Navigation Satellite System (BDS) has completed third phase construction and currently provides global services, with a mixed constellation of BDS-2 and BDS-3. The newly launched BDS-3 satellites are equipped with rubidium and passive hydrogen maser (PHM) atomic clocks. The performance of atomic clocks is one of the cores of satellite navigation system, which will affect the performance of positioning, navigation and timing (PNT). In this paper, we systematically analyze the characteristics of BDS-2 and BDS-3 atomic clocks, based on more than one year of precise satellite clock products and broadcast ephemeris. Firstly, the results of overlapping Allan variations demonstrate that BDS-3 Rb and PHM clocks improve better in stability than BDS-2 Rb clock and are comparable to GPS IIF Rb and Galileo PHM clocks. Accordingly, the STDs of BDS-3 broadcast satellite clock are better than GPS and BDS-2, which are at the same level with that of Galileo. Secondly, the inter-system bias (ISB) between BDS-2 and BDS-3 is analyzed by satellite clock datum comparison and precise point positioning (PPP). Surprisingly, the discrepancy between BDS-2 and BDS-3 satellite clock datum has a great difference between products that could reach up to about 10 ns for WHU satellite clock products and broadcast ephemeris. Moreover, the ISBs between BDS-2 and BDS-3 satellite clocks are quite stable over one-year periods. Thirdly, due to the improved stability of BDS-3 atomic clock, the 68% positioning accuracy is better than 0.65 m at 10 min for BDS-3 PPP, based on broadcast ephemeris. Besides, the non-negligible bias between BDS-2 and BDS-3 will greatly affect the BDS precise data processing. The accuracy of positioning is greatly improved when considering the ISB.
Highlights
The BeiDou Navigation Satellite System (BDS), independently constructed and developed by China, has been fully completed, following the “three-step” development strategy, as of 31 July 2020, and currently consists of a mixed constellation of BDS-2 and BDS-3 [1,2].In 2012, the BDS-2, as the second phase started providing positioning, navigation and timing (PNT) services to the Asia Pacific region [3,4], which is formed by a 15 satellite constellation, including 5 satellites in geostationary Earth orbit (GEO), 7 satellites in inclined geosynchronous orbit (IGSO) and 3 satellites in medium Earth orbit (MEO)
We focus on evaluation of BDS different satellite clock products with an emphasis on the effect of inter-system bias (ISB) between BDS-2 and BDS-3, including BDS clock stabilities and accuracy assessment, based on Allan deviation, the long-term characteristics of ISB
The BDS-3 positioning performs significantly better compared with GPS under the same satellite number nearly, especially in vertical
Summary
The BeiDou Navigation Satellite System (BDS), independently constructed and developed by China, has been fully completed, following the “three-step” development strategy, as of 31 July 2020, and currently consists of a mixed constellation of BDS-2 and BDS-3 [1,2]. The broadcast ephemeris of satellite atomic clocks with better stabilities can provide more accurate prediction of clock offsets and provide users with better PNT services and even precise point positioning (PPP) services. The datum of precise clock products generated by international GNSS service (IGS) analysis centers (ACs) may exist a systematic bias for BDS-2 and BDS-3, since there are many receiver types in MGEX networks, such as TRIMBLE, SEPT and JAVAD, etc. Prior studies of the ISB between BDS-2 and BDS-3 have mostly been based on the results of PPP and focused on the impact of positioning and time transfer [31,32,33], while few touch upon the long-term characteristics of different satellite clock products. The PPP performance, based on broadcast ephemeris, are evaluated and compared for five strategies
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